A drug delivery system (DDS) has been extensively studied. In recent years, the results of controlled release of protein drugs have been reported (see Mundargi R. C., et al. Journal of Controlled Release, 2008, Vol. 125, pp. 193-209).
However, previous studies focus on suspended release of a drug over a long time, and a method that can implement in situ controlled release (e.g., release start timing) of a drug in vivo has not been reported.
For example, stem cell transplantation has been considered to be promising for the treatment of intractable diseases, and a number of studies have been conducted.
It has been considered that the progression of Parkinson's disease (i.e., central nervous system disease) can be stopped by drug therapy or the like, but a complete cure can be achieved only by neural stem/progenitor cell transplantation. Therefore, development of stem cell transplantation therapy has been strongly desired.
However, current stem cell transplantation therapy has a problem in that damaged tissue may not be able to control the transplanted stem cells, and may not be regenerated.
Although various methods have been studied, an effective method has not yet been developed.
It is well-known from molecular biological findings that stem cell differentiation is efficiently induced stepwise by a plurality of factors.
Specifically, it is indispensable to utilize the actions of a plurality of factors (e.g., factors A and B) stepwise at the desired timings in order to efficiently induce stem cell differentiation.
However, a protein DDS that can cause the functional factor to effect its action at the desired timing has not been developed.
This is considered to be because the major object of previous studies is to deliver proteins to the desired position, and effect suspended release of the proteins near the target cells (i.e., it has not been desired to control the action timing).
The inventors of the invention conducted studies in order to develop a protein delivery material that can implement in situ control of differentiation induction on the assumption that neural stem/progenitor cell transplantation therapy for the treatment of Parkinson's disease will make substantial progress through development of a material by which differentiation of transplanted stem cells can be efficiently induced, and tissue can be regenerated. The inventors thus developed the composition according to the invention.